Aluminum alloys with high strength and cosmetic appeal

ABSTRACT

The disclosure provides an aluminum alloy including having varying ranges of alloying elements. In various aspects, the alloy has a wt % ratio of Zn to Mg ranging from 4:1 to 7:1. The disclosure further includes methods for producing an aluminum alloy and articles comprising the aluminum alloy.

PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 14/502,943, entitled Aluminum Alloys with High Strength andCosmetic Appeal”, filed on Sep. 30, 2014, which claims the benefit under35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No.61/884,860, entitled “Aluminum Alloys with High Strength and CosmeticAppeal”, filed on Sep. 30, 2013, and U.S. Provisional Patent ApplicationNo. 62/047,600, entitled “Aluminum Alloys with High Strength andCosmetic Appeal”, filed on Sep. 8, 2014, each of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

Embodiments described herein generally relate to aluminum alloys. Morespecifically, the embodiments relate to aluminum alloys with highstrength and cosmetic appeal for applications including enclosures forelectronic devices.

BACKGROUND

Commercial aluminum alloys, such as the 6063 aluminum (Al) alloy, havebeen used for fabricating enclosures for electronic devices. However,the 6063 aluminum alloy has relatively low yield strength, for example,about 214 MPa, which may dent easily when used as an enclosure forelectronic devices. It may be desirable to produce alloys with highyield strength such that the alloys do not dent easily. The electronicdevices may include mobile phones, tablet computers, notebook computers,instrument windows, appliance screens, and the like.

Many commercial 7000 series aluminum alloys have been developed foraerospace applications. Generally, 7000 series aluminum alloys have highyield strengths. However, commercial 7000 series aluminum alloys are notcosmetically appealing when used to make enclosures for electronicdevices. For example, commercial 7000 aluminum alloys normally containzirconium (Zr) and copper (Cu) to strengthen the alloys. Although Custrengthens the alloys, the Cu-containing aluminum alloys normallyexhibit yellowish color after being anodized. The yellowish color is notcosmetically appealing. FIG. 1 depicts an image of an alloy fabricatedwith a commercial aluminum alloy containing Cu. The color of the alloyis yellowish.

Cosmetic appeal is very important for enclosures for electronic devices.The high yield strength is also important to help resist denting. Thecommercial alloys (e.g. 2000, 6000, or 7000 series alloys) do notachieve both high yield strength and cosmetic appeal, such as a neutralcolor, after anodizing and blasting.

There still remains a need to develop aluminum alloys with high strengthand improved cosmetics.

SUMMARY

Aspects and embodiments described herein may provide aluminum alloyswith high strength and improved cosmetics.

In some aspects, the disclosure is directed to an aluminum alloyincluding: 4.0 to 10.0 wt % Zn, 0.5 to 2.0 wt % Mg, 0 to 0.50 wt % Cu,and 0 to 0.10 wt % Zr, with the balance being aluminum and incidentalimpurities.

In various aspects, the alloy can have a wt % ratio of Zn to Mg from 4:1to 7:1.

In various aspects, the aluminum alloy includes 4.25 to 6.25 wt % Zn and0.75 to 1.50 wt % Mg.

In various aspects, the aluminum alloy includes 4.75 to 6.25 wt % Zn and0.75 to 1.50 wt % Mg.

In various aspects, the aluminum alloy includes 5.00 to 5.65 wt % Zn and1.00 to 1.10 wt % Mg.

In various aspects, the aluminum alloy includes 5.40-5.60 wt % Zn and0.90-1.10 wt % Mg.

In various aspects, the aluminum alloy includes 5.40 to 5.65 wt % Zn and1.30 to 1.50 wt % Mg.

In various aspects, the aluminum alloy includes 6.40 to 6.60 wt % Zn and1.30 to 1.50 wt % Mg.

In various aspects, the aluminum alloy includes 4.25 to 6.25 wt % Zn and0.75 to 1.50 wt % Mg.

In some aspects, the aluminum alloy includes 4.0 to 10.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.20 wt % Cu, and 0 to 0.10 wt % Zr, the alloy havinga wt % ratio of Zn to Mg from 4:1 to 7:1.

In some aspects, the aluminum alloy includes 4.0 to 10.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.20 wt % Cu, and 0 to 0.10 wt % Zr, the alloy havinga wt % ratio of Zn to Mg from 4:1 to 7:1.

In some aspects, the aluminum alloy includes 4.0 to 8.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.01 wt % Cu, and 0 to 0.01 wt % Zr, the alloy havinga wt % ratio of Zn to Mg from 4:1 to 7:1.

In some aspects, the aluminum alloy includes 4.0 to 8.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.50 wt % Cu, and 0 to 0.10 wt % Zr. In certainfurther aspects, the alloy can have a wt % ratio of Zn to Mg from 4:1 to7:1.

In some aspects, the aluminum alloy includes 4.0 to 8.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.20 wt % Cu, and 0 to 0.10 wt % Zr. In certainfurther aspects, the alloy can have a wt % ratio of Zn to Mg from 4:1 to7:1.

In some aspects, an aluminum alloy includes 4.0 to 8.0 wt % Zn, 0.5 to2.0 wt % Mg, 0 to 0.01 wt % Cu, and 0 to 0.01 wt % Zr, the alloy havinga wt % ratio of Zn to Mg from 4:1 to 7:1.

In some aspects, an aluminum alloy includes 5.25 to 5.75 wt % Zn, 1.0 to1.4 wt % Mg, 0 to 0.01 wt % Cu, and 0 to 0.010 wt % Zr.

In some aspects, a method is provided for producing an aluminum alloy.The method includes forming a melt that comprises 4.0 to 8.0 wt % Zn,0.5 to 2.0 wt % Mg, 0 to 0.01 wt % Cu, and 0 to 0.01 wt % Zr. The alloyhas a wt % ratio of Zn to Mg ranging from 4:1 to 7:1. The method alsoincludes cooling the melt to room temperature. The method furtherincludes homogenizing the cooled alloy by heating to an elevatedtemperature and holding at the elevated temperature for a period.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification, or may belearned by the practice of the embodiments discussed herein. A furtherunderstanding of the nature and advantages of certain embodiments may berealized by reference to the remaining portions of the specification andthe drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Further non-limiting aspects of the disclosure are described byreference to the drawings and descriptions.

FIG. 1 depicts an image of a MacBook fabricated with an aluminum alloycontaining Cu in a quantity of 0.2% or greater.

FIG. 2 depicts the composition space of magnesium (Mg) versus zinc (Zn))for Al—Zn—Mg alloys, in accordance with embodiments of the disclosure.

FIG. 3 is an image showing long grain structure of Zr-containingaluminum alloys, in accordance with embodiments of the disclosure.

FIG. 4 is an image showing fine grain structure of Zr-free aluminumalloys, in accordance with embodiments of the disclosure.

FIG. 5 shows the hardness of a sample alloy disclosed herein as comparedto a 6063 aluminum alloy using different quenching methods, inaccordance with embodiments of the disclosure.

DETAILED DESCRIPTION

The disclosure may be understood by reference to the following detaileddescription, taken in conjunction with the drawings as described below.It is noted that, for purposes of illustrative clarity, certain elementsin various drawings may not be drawn to scale, may be representedschematically or conceptually, or otherwise may not correspond exactlyto certain physical configurations of embodiments.

The present patent application is directed to 7xxx series aluminumalloys having, in various embodiments, increased hardness, improvedcosmetic appeal, and/or more efficient processing parameters. The Alalloys can be described by various wt % of elements, as well as specificproperties. In all descriptions of the alloys described herein, it willbe understood that the wt % balance of alloys is Al and incidentalimpurities.

In some aspects, a composition having an amorphous alloy can include asmall amount of incidental impurities. The impurity elements can be canbe present, for example, as a byproduct of processing and manufacturing.The impurities can be less than or equal to about 2 wt %, alternativelyless than or equal about 1 wt %, alternatively less than or equal about0.5 wt %, alternatively less than or equal about 0.1 wt %.

In some aspects, the disclosure provides aluminum alloys with hightensile yield strength of at least 280 MPa. In additional aspects, thedisclosure provides aluminum alloys with a tensile yield strength of atleast 350 MPa. The alloys include zinc (Zn) and magnesium (Mg)strengthen the alloys.

Zinc and Magnesium

The alloys can be strengthened by the addition of Zn and Mg. Zn and Mgprecipitate as MgZn₂ to form a second MgZn₂ phase in the alloy. Thissecond MgZn₂ phase can increase the strength of the alloy byprecipitation strengthening. In various aspects, MgZn₂ precipitates canbe produced from processes including rapid quenching and subsequent heattreatment, as described herein.

The yield strengths of the alloys can be increased by increasing the Zncontent. However, resistance to stress corrosion cracking may decreasewith increasing Zn content. Zn content may vary depending on thedesigned stress corrosion resistance and designed yield strength. Highyield strength may trade off with lower corrosion resistance for thealloys. For example, for high corrosion resistance alloys, Zn contentmay be lower than for low corrosion resistant alloys, depending on theapplications. In variations in which high strength alloys haverelatively low stress corrosion resistance, Zn content may be higherthan the high corrosion resistant alloys.

The amount of Zn and Mg in the alloy can be selected at stoichiometricamounts such that all available Mg and Zn are used to form MgZn₂ in thealloy. In some embodiments, the Zn and Mg is in a molar ratio such thatno excess Mg or Zn is present outside of MgZn₂. In various embodiments,some excess Zn or Mg may be present.

In some embodiments, the alloys include Zn less than 10.0 wt %. In someembodiments, the alloys include Zn less than 9.5 wt %. In someembodiments, the alloys include Zn less than 9.0 wt %. In someembodiments, the alloys include Zn less than 8.5 wt %. In someembodiments, the alloys include Zn less than 8.0 wt %. In someembodiments, the alloys include Zn less than 7.5 wt %. In someembodiments, the alloys include Zn less than 7.0 wt %. In someembodiments, the alloys include Zn less than 6.5 wt %. In someembodiments, the alloys include Zn less than 6.0 wt %. In someembodiments, the alloys include Zn less than 5.5 wt %. In someembodiments, the alloys include Zn less than 5.0 wt %. In someembodiments, the alloys include Zn less than 4.5 wt %.

In some embodiments, the alloys include Zn greater than 4.0 wt %. Insome embodiments, the alloys include Zn greater than 4.5 wt %. In someembodiments, the alloys include Zn greater than 5.0 wt %. In someembodiments, the alloys include Zn greater than 5.5 wt %. In someembodiments, the alloys include Zn greater than 6.0 wt %. In someembodiments, the alloys include Zn greater than 6.5 wt %. In someembodiments, the alloys include Zn greater than 7.0 wt %. In someembodiments, the alloys include Zn greater than 7.5 wt %. In someembodiments, the alloys include Zn greater than 8.0 wt %. In someembodiments, the alloys include Zn greater than 8.5 wt %. In someembodiments, the alloys include Zn greater than 9.0 wt %. In someembodiments, the alloys include Zn greater than 9.5 wt %.

In some embodiments, the alloys include Zn from 4.0 to 8.0 wt %. In someembodiments, the alloys have from 4.25 to 6.25 wt % Zn. In someembodiments, the alloys have less than 6.25 wt % Zn. In someembodiments, the alloys include Zn ranging from 5.25 to 5.75 wt %. Insome embodiments, the alloys include Zn less than 6.25 wt %. In someembodiments, the alloys include Zn less than 6.00 wt %. In someembodiments, the alloys include Zn less than 5.75 wt %. In someembodiments, the alloys include Zn less than 5.65 wt %. In someembodiments, the alloys include Zn less than 5.55 wt %. In someembodiments, the alloys include Zn less than 5.45 wt %. In someembodiments, the alloys include Zn less than 5.35 wt %. In someembodiments, the alloys include Zn less than 5.25 wt %. In someembodiments, the alloys include Zn less than 5.00 wt %. In someembodiments, the alloys include Zn less than 5.75 wt %. In someembodiments, the alloys include Zn less than 4.75 wt %. In someembodiments, the alloys include Zn less than 4.50 wt %.

In some embodiments, the alloys include Zn greater than 4.25 wt %. Insome embodiments, the alloys include Zn greater than 4.50 wt %. In someembodiments, the alloys include Zn greater than 4.75 wt %. In someembodiments, the alloys include Zn greater than 5.00 wt %. In someembodiments, the alloys include Zn greater than 5.25 wt %. In someembodiments, the alloys include Zn greater than 5.35 wt %. In someembodiments, the alloys include Zn greater than 5.45 wt %. In someembodiments, the alloys include Zn greater than 5.55 wt %. In someembodiments, the alloys include Zn greater than 5.65 wt %. In someembodiments, the alloys include Zn greater than 5.75 wt %. In someembodiments, the alloys include Zn greater than 6.00 wt %.

In some embodiments, the alloys can be designed to have Zn to Mg (Zn/Mg)weight ratio of approximately 11:2, such that MgZn₂ particles orprecipitates can be formed and distributed in the Al to strengthen thealloy. In some embodiments, the Zn/Mg weight ratio can range from 4:1 to7:1. In some embodiments, maintaining this ratio of Zn/Mg can reduceexcessive Zn to improve stress corrosion resistance for the alloys.

In some embodiments, the alloys include Mg from 0.5 to 2.0 wt %. In someembodiments, the alloys include Mg less than 2.0%. In some embodiments,the alloys include Mg from 0.75 to 1.50 wt %. In some embodiments, thealloys include Mg from 1.00 to 1.10 wt % Mg. In some embodiments, thealloys include Mg less than 2.0%. In some embodiments, the alloysinclude Mg less than 1.75%. In some embodiments, the alloys include Mgless than 1.5%. In some embodiments, the alloys include Mg less than1.0%. In some embodiments, the alloys include Mg greater than 0.5%. Insome embodiments, the alloys include Mg greater than 0.75%. In someembodiments, the alloys include Mg greater than 1.0%. In someembodiments, the alloys include Mg greater than 1.5%.

Copper

The alloys can be free of copper (Cu) such that the alloys does notexhibit yellowish color. The alloy is thereby more cosmeticallyappealing by having a neutral color after anodizing. Those skilled inthe art will understand alloys that “eliminate Cu,” are “Cu free,” orthat have 0 wt % Cu to mean that the amount of Cu in an alloy does notcontain more than a naturally occurring abundance of Cu.

In various embodiments, alloys disclosed herein can be designed to havereduced Cu or be free of Cu to reduce and/or eliminate the undesirableyellowish color after anodizing. The alloys can increase Zn and Mgcontent to compensate for the loss in the yield strengths of the alloysdue to elimination or reduction of Cu and or Zr elements in the alloys.

The presence of Cu in 7xxx Al alloys can increase yield strength ofalloys, but can have a deleterious effect on cosmetic appeal. Withoutwishing to be limited to a particular mechanism or mode of action, Cumay provide stability to Mg₂Zn particles. It will be understood that thequantity of Cu in the alloy can be of an amount described herein. Invarious alloys of the disclosure, the presence of Cu up to 0.01 wt %,alternatively 0.05 wt %, and alternatively up to 0.15 wt %, provides forincreased yield strength without loss of neutral color on the L* a* b*scale, as described herein.

In various aspects, the addition of Cu reduces the need for Zn in thealloy. As the wt % of Cu increases, the amount of Zn can be reduced.Further, without wishing to be limited to any theory or mode of action,the presence of Cu in the alloys of the disclosure provides increasedstability Mg₂Zn. The amount of Cu in such alloys up to 0.01 wt %, up to0.10 wt %, alternatively up to 0.15 wt %, such that the Al alloy has aneutral color as described herein (e.g. with respect to the L*a*b*values).

In some embodiments, the alloys include Cu from 0 to 0.01 wt %. In someembodiments, the alloys include Cu less than 0.01 wt %. In someembodiments, the alloys include Cu greater than 0 wt %.

In some aspects, the alloys can have Cu less than 0.30 wt %. In someaspects, the alloys can have Cu less than 0.20 wt %. In various aspects,the alloys can have Cu in an amount greater than 0.10 wt %. In variousaspects, the alloys can have Cu in an amount greater than 0.05 wt %. Invarious aspects, the alloys can have Cu in an amount greater than 0.04wt %. In various aspects, the alloys can have Cu in an amount greaterthan 0.03 wt %. In various aspects, the alloys can have Cu in an amountgreater than 0.02 wt %. In various aspects, the alloys can have Cu in anamount greater than 0.01 wt %.

In various embodiments, the yield strength of the alloy is at least 275mPA. In certain embodiments, the yield strength of the alloy is at least280 mPA. In certain embodiments, the yield strength of the alloy is atleast 300 mPA. In certain embodiments, the yield strength of the alloyis at least 320 mPA. In certain embodiments, the yield strength of thealloy is at least 330 mPA. In certain embodiments, the yield strength ofthe alloy is at least 340 mPA. In certain embodiments, the yieldstrength of the alloy is at least 350 mPA. In some embodiments, thealloys have a yield strength of at least 350 MPa. In some embodiments,the alloys have a yield strength of at least 360 MPa. In someembodiments, the alloys have a yield strength of at least 370 MPa. Insome embodiments, the alloys have a yield strength of at least 380 MPa.In some embodiments, the alloys have a yield strength of at least 390MPa. In some embodiments, the alloys have a yield strength of at least400 MPa. In some embodiments, the alloys have a yield strength of atleast 410 MPa. In some embodiments, the alloys have a yield strength ofat least 420 MPa. In some embodiments, the alloys have a yield strengthof at least 430 MPa. In some embodiments, the alloys have a yieldstrength of at least 440 MPa. In some embodiments, the alloys have ayield strength of at least 450 MPa.

Iron

In various aspects, the wt % of Fe in the alloys described herein can belower than that for conventional 7xxx series aluminum alloys. Bycontrolling the Fe level to be at the disclosed quantities, the alloyscan appear less dark, i.e. have a lighter color, after anodizationtreatment, and possess fewer coarse particle defects. The reduction inFe (and Si) reduces the volume fraction of course particles, whichimproves the cosmetic qualities, for example distinctness of image(“DOI”) and Haze as described herein, after anodization.

The wt % of Fe can help the alloy maintain a fine grain structure.Alloys with a small trace of Fe also have a neutral color afteranodizing.

In some variations, the alloy has equal to or less than 0.30 wt % Fe. Insome variations, the alloy has equal to or less than 0.25 wt % Fe. Insome variations, the alloy has equal to or less than 0.20 wt % Fe. In afurther variation, Fe has equal to or less than 0.12 wt %. In someembodiments, the alloys include Fe equal to or less than 0.10 wt %. Insome embodiments, the alloys include Fe equal to or less than 0.08 wt %.In some variations, the alloy includes Fe equal to or less than 0.06 wt%.

In some embodiments, the alloys include Fe greater than 0.04 wt %. Insome embodiments, the alloys include Fe greater than 0.06 wt %. In someembodiments, the alloys include Fe greater than 0.08 wt %. In someembodiments, the alloys include Fe greater than 0.10 wt %. In someembodiments, the alloys include Fe from 0.04 to 0.25 wt %. In someembodiments, the alloys include Fe from 0.04 to 0.12 wt %. Such wt % ofFe allows maintenance of a fine grain structure.

Zirconium

Conventional 7xxx series aluminum alloys include Zr to increase hardnessof the alloy. The presence of Zr in conventional 7xxx series alloysproduces a fibrous grain structure in the alloy, and allows the alloy tobe reheated without expanding the grain structure of the alloy. In thealloys disclosed herein, the reduction in or absence of Zr allowssurprising grain structure control at a low average grain aspect ratiofrom sample-to-sample. In addition, reduction or elimination of Zr inthe alloy can reduce elongated grain structures and/or streaky lines infinished products.

In various embodiments, the Al alloys can also be Zr-free. Those skilledin the art will understand alloys that “eliminate Zr” or“Zr free” tomean that the amount of Zr in an alloy does not contain more than anaturally occurring abundance of Zr.

In some embodiments, the alloys include Zr from 0 to 0.001 wt %. In someembodiments, the alloys include Zr less than 0.001 wt %. In someembodiments, the alloys include Zr greater than 0 wt %. In someembodiments, the alloy can have up to 0.01 wt % Zr. In furtherembodiments, the alloy can have up to 0.02 wt % Zr.

In some embodiments, the alloy can have up to 0.10 wt % Zr. In someembodiments, the alloy can have up to 0.08 wt % Zr. In some embodiments,the alloy can have up to 0.06 wt % Zr. In some embodiments, the alloycan have less than 0.05 wt % Zr. In some embodiments, the alloy can haveless than 0.04 wt % Zr. In some embodiments, the alloy can have lessthan 0.03 wt % Zr. In some embodiments, the alloy can have less than0.02 wt % Zr. In some embodiments, the alloy can have less than 0.01 wt% Zr. In some embodiments, the alloy can have greater than 0.01 wt % Zr.In some embodiments, the alloy can have greater than 0.02 wt % Zr. Insome embodiments, the alloy can have greater than 0.03 wt % Zr. In someembodiments, the alloy can have greater than 0.04 wt % Zr. In someembodiments, the alloy can have greater than 0.05 wt % Zr. In someembodiments, the alloy can have greater than 0.06 wt % Zr. In someembodiments, the alloy can have greater than 0.08 wt % Zr.

The alloys can also have good corrosion resistance, which helps maintainan appealing cosmetic appearance in harsh environments.

The alloys can also have a thermal conductivity of at least 150 W/mK,which helps heat dissipation of the electronic devices. The alloys canbe strengthened by solid solution. Zn and Mg may be soluble in thealloys. Solid solution strengthening can improve the strength of a puremetal. In this alloying technique, atoms of one element, e.g. analloying element, may be added to the crystalline lattice of anotherelement, e.g. a base metal. The alloying element is contained with thematrix, forming a solid solution.

The wt % concentrations of Zr and Fe in the alloys disclosed hereinprovide for control of grain structure. In conventional 7xxx series Alalloys, grain size can increase during heat treatment after extrusion.In conventional 7xxx alloys with larger Zr concentrations, graininflation can produce grains that are more fibrous and visible,producing incongruities that are cosmetically unacceptable. Such grainshave aspect ratios outside the range of various alloys disclosed herein(e.g between 1.0:0.80 and 1.0:1.2). Further, the resulting alloys canhave deficits in yield strength, hardness, and/or cosmetics.

Various 6063 Al alloys that are Zr free and have at least 0.10 wt % Feallow for controlled grain size of during manufacturing. In various such6063 alloys, a 0.08 wt % of Fe results in grain size to becomeunpredictably large. In the presently disclosed alloys, reduced oreliminated Zr combined with low wt % Fe allow for grain size control.

Iron and Silicon

The disclosed alloys provide improved lightness and clarity incombination with increased yield strength and hardness over conventionalalloys. In conventional 7xxx Al alloys, high wt % Fe and/or Si canresult in poor anodization and cosmetics. In the alloys disclosedherein, low Fe and Si result in fewer inclusions that disrupt clarityfollowing anodization. As a result, the alloys described herein haveimproved clarity.

In some embodiments, the alloys include up to 0.20 wt % Si. In someembodiments, the alloys include Si from 0.03 to 0.05 wt %. In someembodiments, the alloys include Si less than 0.05 wt %. In someembodiments, the alloys include Si less than 0.04 wt %. In someembodiments, the alloys include Si greater than 0.03 wt %. In someembodiments, the alloys include Si greater than 0.04 wt %.

In various other aspects, the Al alloys disclosed herein can include Ag.In some aspects, the alloys can include greater than 0.01 wt % Ag. Infurther aspects, the Al alloys can include no more than 0.1 wt % Ag. Infurther aspects, the Al alloys can include no more than 0.2 wt % Ag. Infurther aspects, the Al alloys can include no more than 0.3 wt % Ag. Infurther aspects, the Al alloys can include no more than 0.4 wt % Ag. Infurther aspects, the Al alloys can include no more than 0.5 wt % Ag.

In various additional embodiments, additionally elements can be added tothe alloy in amounts that do not exceed 0.050 wt % per element. Examplesof such elements include one or more of Ca, Sr, Sc, Y, La, Ni, Ta, Mo,W, Co. Additional elements that do not exceed 0.050 wt % per element, oralternatively 0.100 wt % per element, include Li, Cr, Ti, Mn, Ni, Ge,Sn, In, V, Ga, and Hf.

Standard methods may be used for evaluation of cosmetics includingcolor, gloss and haze. Gloss describes the perception of a surfaceappearing “shiny” when light is reflected. The Gloss Unit (GU) isdefined in international standards including ISO 2813 and ASTM D523. Itis determined by the amount of reflected light from a highly polishedblack glass standard of known refractive index of 1.567. The standard isassigned with a specular gloss value of 100. Haze describes the milkyhalo or bloom seen on the surface of high gloss surfaces. Haze iscalculated using the angular tolerances described in ASTM E430. Theinstrument can display the natural haze value (HU) or Log Haze Value(HU_(L0G)). A high gloss surface with zero haze has a deep reflectionimage with high contrast. DOI (Distinctness Of Image) is, as the nameimplies, a function of the sharpness of a reflected image in a coatingsurface, based on ASTM D5767. Orange peel, texture, flow out and otherparameters can be assessed in coating applications where high glossquality is becoming increasingly important. The measurements of gloss,haze, and DOI may be performed by testing equipment, such as RhopointIQ.

By using the aluminum alloys of the present disclosure, defects viewedthrough the anodized layer were reduced, while maintaining yieldstrength and hardness, thereby providing a high gloss and highdistinctness of image with surprisingly low haze.

High yield strength may also trade off with lower thermal conductivityfor the Al alloys. Generally, Al alloys have lower thermal conductivitythan pure Al. Alloys with higher alloying contents for morestrengthening may have lower thermal conductivity than alloys withreduced alloying contents for less strengthening. For example, the 7xxxseries alloys described herein may have a thermal conductivity greaterthan 130 W/mK. In some embodiments, the modified 7xxx alloy may have athermal conductivity greater than or equal to 140 W/mK. In someembodiments, the modified 7xxx alloy may have a thermal conductivitygreater than or equal to 150 W/mK. In some embodiments, the modified7xxx alloy may have a thermal conductivity greater than or equal to 160W/mK. In some embodiments, the modified 7xxx alloy may have a thermalconductivity greater than or equal to 170 W/mK. In some embodiments, themodified 7xxx alloy may have a thermal conductivity greater than orequal to 180 W/mK. In some embodiments, the modified 7xxx alloy may havea thermal conductivity less than than 140 W/mK. In various embodiments,the alloy may have a thermal conductivity between 190-200 W/mK. Thealloys may have a thermal conductivity of about 130-200 W/mK. In variousembodiments, the alloy may have a thermal conductivity of about 150-180W/mK. For different electronic devices, the designed thermalconductivity and the designed yield strength may vary, depending on thetype of device, such as handheld devices, portable devices, or desktopdevices.

Table 1 lists example alloy compositions and yield strengths for theCu-free aluminum alloys (e.g. alloys having less than 0.01 wt % Cu) incomparison to commercial 7000 series Al alloys and 6063 Al alloy. Samplealloys 1-14 are examples of Al alloys having less than 0.01 wt % Cu. Thealloys were tested for tensile yield strength. The weight ratio of Zn toMg and the color of these alloys are also listed in Table 1.

TABLE 1 Yield Strengths and Compositions of Aluminum Alloys NeutralYield Ratio of color Strength Zn to (blasted Aspect Zn Mg Ag Zr Cu Si Fe(MPa) Mg surface) Ratio Commercial <0.01 0.47-0.55 <0.01 <0.01 <0.010.37-0.44 0.12 max 214 6063 Sample alloy 1 5.5 1.0 — — <0.01 0.030.04-0.08 350 5.5 yes 0.8-1.2 Sample alloy 2 5.5 1.2 — — <0.01 0.030.04-0.08 360 4.6 0.8-1.2 Sample alloy 3 5.5 1.0 0.3 — <0.01 0.030.04-0.08 360 5.5 0.8-1.2 Sample alloy 4 5.5 1.8 0.3 — <0.01 0.030.04-0.08 415 3.1 0.8-1.2 Sample alloy 5 4.5 1.8 0.3 — <0.01 0.030.04-0.08 380 2.5 0.8-1.2 Sample alloy 6 4.5 1.6 0.3 — <0.01 0.030.04-0.08 350 2.8 0.8-1.2 Sample alloy 7 5.5 1.4 — — <0.01 0.03 .20 3503.9 yes 0.8-1.2 Sample alloy 8 6.2 1.7 — — <0.01 0.03 .20 380 3.6 yes0.8-1.2 Sample alloy 9 6.7 1.7 <0.01 0.03 .20 390 3.9 0.8-1.2 Samplealloy 10 6.5 1.4 — — <0.01 0.05 0.06 360 4.6 0.8-1.2 Sample alloy 117.5-8.1 1.7-1.8 — — <0.01 0.03 0.08-0.11 470 4.2-4.8 yes 0.8-1.2 Samplealloy 12 5.5 1.4 — — <0.01 0.05 0.08-0.11 350 3.9 yes 0.8-1.2 Samplealloy 13 5.5 1.4 —  0.12 <0.01 0.05 0.08-0.11 400 3.9 yes 0.8-1.2 Samplealloy 14 7.5 1.7 — — <0.01 0.05 0.08 470 4.4 0.8-1.2 Sample alloy 155.45 1.05 — — 0.05 0.03 0.04-0.08 350 5.2 yes 0.8-1.2 Sample alloy 165.35 1.05 — — 0.10 0.03 0.04-0.08 350 5.05 yes 0.8-1.2 Sample alloy 175.25 1.05 — — 0.15 0.03 0.04-0.08 350 5.0 yes 0.8-1.2 Sample alloy 185.10 1.05 — — 0.20 0.03 0.04-0.08 350 MPa 4.85 yes 0.8-1.2 Sample Alloy19 5.5 1.05 — — <0.01 0.03 0.04-0.08 350 5.5 yes 0.8-1.2 Commercial5.0-6.5 0.5-1.0 <0.40 0.05-0.25 <0.20 <0.30 <0.35 290  5.0-13.0 alloyAA7003 Commercial 4.0-5.0 1.0-1.8 — 0.08-0.20 <0.10 <0.35 <0.40 3452.2-5.0 alloy AA7005 Commercial 4.5-5.5 0.7-1.4 — 0.12-0.25 <0.05 <0.10<0.10 350 3.2-79 alloy AA7108

The balance of each alloy in Table 1 is Al and incidental impurities.

As depicted in Table 1, the commercial Al 6063 alloy includes less than0.01 wt % Zn, 0.47-0.55 wt % Mg, 0.37-0.44 wt % Si, and 0.12 wt % Fe,and has a measured yield strength of about 214 MPa. The commercial 6063Al alloy has a significantly lower yield strength than the measuredyield strength of 350 MPa and all the other alloys, which have anincreased Zn and Mg content.

Sample alloy 1 includes 5.5 wt % Zn, 1.0 wt % Mg, and has a yieldstrength of about 350 MPa. Sample alloy 2 includes 5.5 wt % Zn, 1.2 wt %Mg, and has a yield strength of about 360 MPa. By increasing the Mgcontent from 1.0 wt % of sample alloy 1 to 1.2 wt % of sample alloy 2,the yield strength slightly increases from 350 MPa to 360 MPa. Thissuggests that higher Mg content can increase the yield strength.

In another variation, the alloy can include from 5.40-5.60 wt % Zn andfrom 0.90-1.10 wt % Mg. In various embodiments, the alloy can includefrom 5.4-5.6 wt % Zn, from 0.9-1.1 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.04-0.08 wt % Fe, with the balance Al andincidental impurities. In further embodiments, the alloy can includefrom 5.4-5.6 wt % Zn, from 1.1-1.3 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.04-0.08 wt % Fe, with the balance Al andincidental impurities. In various further embodiments, the alloy caninclude from 5.4-5.6 wt % Zn, from 0.9-1.3 wt % Mg, less than 0.01 wt %Cu, from 0.02-0.04 wt % Si, and from 0.04-0.08 wt % Fe, with the balanceAl and incidental impurities.

In some embodiments, the alloys may include silver (Ag), which maystrengthen the alloys. The sample alloys 3-6 have yield strengthsranging from 350 MPa to 415 MPa.

Sample alloy 4 includes 5.5 wt % Zn, 1.8 wt % Mg, 0.3 wt % Ag, with thebalance Al and incidental impurities, and has the highest yield strengthof 415 MPa among the four sample alloys 3-6. Sample alloy 5 includes 4.5wt % Zn, 1.8 wt % Mg, 0.3 wt % Ag, with the balance Al and incidentalimpurities and has the second highest yield strength of 380 MPa amongthe four sample alloys 3-6. Comparing sample alloys 4 and 5, the contentof Mg and Ag remain unchanged while Zn content is increased from 4.5 wt% of sample alloy 5 to 5.5 wt % of sample alloy 4 such that the yieldstrength increases from 380 MPa to 415 MPa. This suggests that higher Zncontent can increase the yield strength of the alloy.

Sample alloy 3 includes 5.5 wt % Zn, 1.0 wt % Mg, and 0.3 wt % Ag, andhas a yield strength of about 360 MPa, while sample alloy 6 includes 4.5wt % Zn, 1.6 wt % Mg, and 0.3 wt % Ag, and has a yield strength of about350 MPa. This suggests that either higher Mg content (e.g. 1.6 wt % Mg)combined with lower Zn content (e.g. 4.5 wt %) or higher Zn content(e.g. 5.5 wt %) combined with lower Mg content (e.g. 1.0 wt %) canincrease the yield strength of the alloys.

Comparing sample alloy 3 to sample alloy 1, the addition of 0.3 wt % Agincreases the yield strength slightly from 350 MPa to 360 MPa. Thisdemonstrates that Ag can increase the yield strength of the alloy.

In another variation, the alloy can include from 5.40-5.60 wt % Zn, from0.9-1.1 wt % Mg, 0.2-0.4 wt % Ag, less than 0.01 wt % Cu, from 0.02-0.04wt % Si, and from 0.04-0.08 wt % Fe, with the balance Al and incidentalimpurities. In another variation, the alloy can include from 4.4-4.6 wt% Zn, from 1.7-1.9 wt % Mg, 0.2-0.4 wt % Ag, less than 0.01 wt % Cu,from 0.02-0.04 wt % Si, and from 0.04-0.08 wt % Fe, with the balance Aland incidental impurities. In another variation, the alloy can includefrom 4.4-4.6 wt % Zn, from 1.7-1.9 wt % Mg, 0.2-0.4 wt % Ag, less than0.01 wt % Cu, from 0.02-0.04 wt % Si, and from 0.04-0.08 wt % Fe, withthe balance Al and incidental impurities.

Sample alloy 7 includes 5.5 wt % Zn, 1.4 wt % Mg, and has a yieldstrength of about 350 MPa. Sample alloy 8 includes 6.2 wt % Zn, 1.7 wt %Mg, and has a yield strength of about 380 MPa. Comparing sample alloy 8to sample alloy 7, both Zn and Mg content increase, such that the yieldstrength increases by 30 MPa to 380 MPa.

Furthermore, sample alloy 9 includes 6.7 wt % Zn, 1.7 wt % Mg, and has ayield strength of about 390 MPa. Comparing sample alloy 9 to samplealloy 8, the Zn content slightly increases by 0.5 wt %, which results aslight increase of 10 MPa in the yield strength of the alloy.

In further variations, the alloy can include from 5.40-5.60 wt % Zn andfrom 1.30-1.50 wt % Mg. In another variation, the alloy can include from5.4-5.6 wt % Zn, from 1.3-1.5 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.01-0.03 wt % Fe, with the balance Al andincidental impurities. In another variation, the alloy can include from6.1-6.3 wt % Zn, from 1.6-1.8 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.01-0.03 wt % Fe, with the balance Al andincidental impurities. In another variation, the alloy can include from6.6-6.8 wt % Zn, from 1.6-1.8 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.01-0.03 wt % Fe, with the balance Al andincidental impurities.

Sample alloy 10 includes 6.5 wt % Zn, 1.4 wt % Mg, and has a yieldstrength of about 360 MPa. Sample alloy 11 includes 7.5-8.1 wt % Zn,1.7-1.8 wt % Mg, and has a yield strength of about 470 MPa. Comparingsample alloy 11 to sample alloy 10, higher Zn content (e.g. 7.5-8.1 wt %Zn) significantly increases the yield strength of the alloy.

In further variations, the alloy can include from 6.40-6.60 wt % Zn andfrom 1.30-1.50 wt % Mg. In another variation, the alloy can include from6.4-6.6 wt % Zn, from 1.3-1.5 wt % Mg, less than 0.01 wt % Cu, from0.04-0.06 wt % Si, and from 0.05-0.07 wt % Fe, with the balance Al andincidental impurities. In another variation, the alloy can include from7.5-8.1 wt % Zn, from 1.6-1.9 wt % Mg, less than 0.01 wt % Cu, from0.02-0.04 wt % Si, and from 0.05-0.07 wt % Fe, with the balance Al andincidental impurities.

Sample alloy 12 includes 5.5 wt % Zn, 1.4 wt % Mg, and has a yieldstrength of about 350 MPa, which is similar to that of sample alloy 7but with the same Zn and Mg content. Although the impurity level of Siis slightly different (0.03 wt % for sample alloy 7 versus 0.05 wt % forsample alloy 12), the yield strength is not affected by such adifference in impurity.

Sample alloy 13 includes 5.5 wt % Zn, 1.4 wt % Mg, 0.12 wt % Zr, and hasa yield strength of about 400 MPa. Comparing sample alloy 13 to samplealloy 12, the addition of 0.12 wt % Zr significantly increases the yieldstrength of the alloy. This demonstrates that the impact of Zr on theyield strengths of the alloys may be significantly higher than Zn, Mg orAg.

Sample alloy 14 includes 7.5 wt % Zn, 1.7 wt % Mg, and has a yieldstrength of about 470 MPa, similar to sample alloy 11. This result isnot surprising, because their Zn and Mg contents are similar.

In further variations, the alloy can include from 5.4-5.6 wt % Zn andfrom 1.3-1.5 wt % Mg. In another variation, the alloy can include from5.4-5.6 wt % Zn, from 1.3-1.5 wt % Mg, less than 0.01 wt % Cu, from0.04-0.06 wt % Si, and from 0.07-0.12 wt % Fe, with the balance Al andincidental impurities. In another variation, the alloy can include from5.4-5.6 wt % Zn, from 1.3-1.5 wt % Mg, 0.11-0.15 wt % Zr, less than 0.01wt % Cu, from 0.04-0.06 wt % Si, and from 0.07-0.12 wt % Fe, with thebalance Al and incidental impurities. In another variation, the alloycan include from 7.4-7.6 wt % Zn, from 1.6-1.8 wt % Mg, less than 0.01wt % Cu, from 0.04-0.06 wt % Si, and from 0.07-0.09 wt % Fe, with thebalance Al and incidental impurities.

Sample alloy 15 includes 5.45 wt % Zn, 1.05 wt % Mg, 0.05 wt % Cu, 0.03wt % Si, from 0.04-0.08 wt % Fe, and had a yield strength of about 350MPa. Sample alloy 16 includes 5.35 wt % Zn, 1.05 wt % Mg, 0.10 wt % Cu,0.03 wt % Si, from 0.04-0.08 wt % Fe, and had a yield strength of about350 MPa. Sample alloy 17 includes 5.25 wt % Zn, 1.05 wt % Mg, 0.15 wt %Cu, 0.03 wt % Si, from 0.04-0.08 wt %,and also had a yield strength ofabout 350 MPa. Sample alloy 18 includes 5.10 wt % Zn, 1.05 wt % Mg, 0.20wt % Cu, and also had a yield strength of about 350 MPa. Sample alloy 19includes 5.50 wt % Zn, 1.05 wt % Mg, Cu less than 0.01 wt %, 0.03 wt %Si, 0.04-0.08 wt % Fe, and also had a yield strength of about 350 MPa.

In another variation, the alloy can include from 5.00-5.65 wt % Zn andfrom 1.00-1.10 wt % Mg. In another variation, the alloy can include from5.35-5.55 wt % Zn, from 0.95-1.15 wt % Mg, from 0.025-0.075 wt % Cu,from 0.02-0.04 wt % Si, and from 0.03-0.10 wt % Fe, with the balance Aland incidental impurities. In another variation, the alloy can includefrom 5.22-5.42 wt % Zn, from 0.95-1.15 wt % Mg, from 0.075-0.125 wt %Cu, from 0.02-0.04 wt % Si, and from 0.03-0.10 wt % Fe, with the balanceAl and incidental impurities. In another variation, the alloy caninclude from 5.12-5.32 wt % Zn, from 0.95-1.15 wt % Mg, from 0.125-0.175wt % Cu, from 0.02-0.04 wt % Si, and from 0.03-0.10 wt % Fe, with thebalance Al and incidental impurities. In another variation, the alloycan include from 5.00-5.20 wt % Zn, from 0.95-1.15 wt % Mg, from0.15-0.25 wt % Cu, from 0.02-0.04 wt % Si, and from 0.03-0.10 wt % Fe,with the balance Al and incidental impurities.

The Al—Zn—Mg alloys differ from the commercial 7000 series aluminumalloys in various aspects discussed herein. The commercial 7000 seriesaluminum alloys normally include Zr and Cu to strengthen the alloys. Forexample, commercial Al alloys 7003, 7005, and 7108 all include Zrranging from 0.05 wt % to 0.25 wt %. As depicted in Table 1, alloy 7003includes 0.05-0.25 wt % Zr, alloy 7005 includes 0.08-0.20 wt % Zr, andalloy 7108 includes 0.12-0.25 wt % Zr. In contrast, various alloys ofthe disclosure that are Zr-free or have a lower amount of Zr can resultin alloys without streaky lines in blasted surface.

In various embodiments, the alloys can be substantially Cu-free. Asshown in Table 1, the sample alloys 1-14 limit Cu to less than 0.01 wt%. The lower quantities of Cu in the alloys may help achieve moreneutral color for an anodized surface than the commercial 7000 series Alalloys. In contrast, commercial Al alloys 7003, 7005, and 7108 allinclude Cu in amounts ranging from 0.05 wt % to 0.2 wt %. For example,as depicted in Table 1, alloy 7003 includes less than 0.20 wt % Cu,alloy 7005 includes less than 0.10 wt % Cu, and alloy 7108 includes lessthan 0.05 wt % Cu.

The alloys also can have lower impurity levels of Fe than commercial7000 series aluminum alloys. The reduced Fe content in the alloys canhelp reduce the number of coarse secondary particles that may compromisethe cosmetic appearance, both before and after anodizing. In contrast,commercial alloys have higher impurity of Fe than the alloys of thedisclosure. For example, as depicted in Table 1, alloy 7003 includesless than 0.35 wt % Fe, alloy 7005 includes less than 0.40 wt % Fe, andalloy 7108 includes less than 0.10 wt % Fe. The resulting DOI and LogHaze are substantially improved in the alloys described herein.

Most sample alloys, such as sample alloys 1, 7, 8, and 10-13, showneutral color. The neutral color may result from limiting the presenceof Cu in the alloys.

As shown in Table 1, the sample alloys 1-12, and 14 all exclude Zr,except sample alloy 13 having 0.12 wt % Zr. The presence of a smallamount of Zr does not affect the neutral color of sample alloy 13, butcan affect the grain structure and thus can lead to streaky lines.

FIG. 2 depicts a graph illustrating the composition space (Mg versus Zn)for the high strength Al—Zn—Mg alloys in accordance with embodiments ofthe disclosure. In some embodiments, the composition space of Mg and Znis from 0 . . . Zr additions inhibit recrystallization and produce along grain structure that can lead to undesirable anodized cosmetics.FIG. 3 is an image showing long grain structure of Zr-containingaluminum alloys. The long grain structure may cause streaky lines, asshown in FIG. 1.

FIG. 4 is an image showing fine grain structure of Zr-free aluminumalloys in accordance with embodiments of the disclosure. The fine grainstructure shown in FIG. 4 does not cause any streaky lines.

In some aspects, the alloy has an average grain aspect ratio less thanor equal to 1:1.5. In some aspects, the alloy has an average grainaspect ratio less than or equal to 1:1.4. In some aspects, the alloy hasan average grain aspect ratio less than or equal to 1:1.3. In someaspects, the alloy has an average grain aspect ratio less than or equalto 1:1.2. In some aspects, the alloy has an average grain aspect ratioless than or equal to 1:1.1. In some aspects, the alloy has an averagegrain aspect ratio less than or equal to 1:1.05. In some aspects, thealloy has an average grain aspect ratio less than or equal to 1:1.04. Insome aspects, the alloy has an average grain aspect ratio less than orequal to 1:1.03. In some aspects, the alloy has an average grain aspectratio less than or equal to 1:1.02. In some aspects, the alloy has anaverage grain aspect ratio less than or equal to 1:1.01. In someaspects, the alloy has an average grain aspect ratio equal to 1:1.

In some aspects, the alloy has an average grain aspect ratio at least0.5:1. In some aspects, the alloy has an average grain aspect ratio atleast 0.6:1. In some aspects, the alloy has an average grain aspectratio at least 0.7:1. In some aspects, the alloy has an average grainaspect ratio at least 0.8:1. In some aspects, the alloy has an averagegrain aspect ratio at least 0.9:1. In some aspects, the alloy has anaverage grain aspect ratio at least 0.95:1. In some aspects, the alloyhas an average grain aspect ratio at least 0.96:1. In some aspects, thealloy has an average grain aspect ratio at least 0.97:1. In someaspects, the alloy has an average grain aspect ratio at least 0.98:1. Insome aspects, the alloy has an average grain aspect ratio at least0.99:1.

The alloys also have reduced impurity level of Si (e.g. 0.03 wt %)compared to commercial 7000 series Al alloys. The reduced Si level mayhelp provide a more cosmetically appealing anodized surface than thealloys with higher Si content in the alloys. In contrast, as depicted inTable 1, commercial alloy 7003 includes less than 0.30 wt % Si,commercial alloy 7005 includes less than 0.35 wt % Si, and commercialalloy 7108 includes less than 0.10 wt % Si.

The yield strengths of the alloys can be higher than the commercial 7000series alloys by increasing the Zn and Mg contents. Although commercial7000 series Al alloys vary in Zn and Mg contents, they have similaryield strengths near 350 MPa. Specifically, alloy 7003 includes 5.0-6.5wt % Zn, 0.5-1.0 wt % Mg. A tensile yield strength of 290 MPa isreported for the commercial 7003 alloy. Commercial alloy 7005 includes4.0-5.0 wt % Zn, 1.0-1.8 wt % Mg, and a yield strength of about 345 MPa.Commercial alloy 7108 includes 4.5-5.5 wt % Zn, 0.7-1.4 wt % Mg, and ayield strength of about 350 MPa.

Processing Methods

In some embodiments, a melt for an alloy can be prepared by heating thealloy, including the composition, as depicted in Table 1. After the meltis cooled to room temperature, the alloys may go through various heattreatments, such homogenization, extruding, forging, aging, and/or otherforming or solution heat treatment techniques.

For the alloys, the MgZn₂ phase may be both within the grains and at thegrain boundary. The MgZn₂ phase may constitute about 3 vol % to about 6vol % of the alloys. MgZn₂ may be formed as discrete particles and/orlinked particles. Various heat treatments can be used to guide theformation of MgZn₂ as discrete particles, rather than linked particles.In various aspects, discrete particles can result in betterstrengthening than linked particles.

In some embodiments, the cooled alloy can be homogenized by heating toan elevated temperature, such as at 500° C., and holding at the elevatedtemperature for a period of time, such as for about 8 hours. It will beappreciated by those skilled in the art that the heat treatmentconditions (e.g. temperature and time) may vary. Homogenization refersto a process in which high-temperature soaking is used at an elevatedtemperature for a period of time. Homogenization can reduce chemical ormetallurgical segregation, which may occur as a natural result ofsolidification in some alloys. In some embodiments, the high-temperaturesoaking is conducted for a dwell time, e.g. from about 4 hours to about48 hours. It will be appreciated by those skilled in the art that theheat treatment condition (e.g. temperature and time) may vary.

In some embodiments, the homogenized alloy can be hot-worked, e.g.,extruded. Extrusion is a process for converting a metal ingot or billetinto lengths of uniform cross section by forcing the metal to flowplastically through a die orifice.

In some embodiments, the hot-worked alloys can be solution heat-treatedat elevated temperatures above 450° C. for a period of time, e.g. 2hours. The solution heat treatments can alter the strength of the alloy.

After the solution-heat treatment, the alloy can be aged at a firsttemperature and time, e.g. 100° C. for about 5 hours, then heated to asecond temperature for a second period of time, e.g. 150° C. for about 9hours, and then quenched with water. Aging is a heat treatment at anelevated temperature, and may induce a precipitation reaction to formprecipitates MgZn₂. In some embodiments, aging may be conducted at afirst temperature for a first period of time and followed at a secondtemperature for a second period of time. Single temperature heattreatments may also be used, for example, at 120° C. for 24 hours. (e.g.temperature and time). It will be appreciated by those skilled in theart that the heat treatment condition (e.g. temperature and time) mayvary.

In further embodiments, the alloy may be optionally subjected to astress-relief treatment between the solution heat-treatment and theaging heat-treatment. The stress-relief treatment can include stretchingthe alloy, compressing the alloy, or combinations thereof.

In some embodiments, the alloys can be anodized. Anodizing is a surfacetreatment process for metal, most commonly used to protect aluminumalloys. Anodizing uses electrolytic passivation to increase thethickness of the natural oxide layer on the surface of metal parts.Anodizing may increase corrosion resistance and wear resistance, and mayalso provide better adhesion for paint primers and glues than baremetal. Anodized films may also be used for cosmetic effects, forexample, it may add interference effects to reflected light.

In some embodiments, the alloys can form enclosures for the electronicdevices. The enclosures may be designed to have a blasted surfacefinish, or an absence of streaky lines. Blasting is a surface finishingprocess, for example, smoothing a rough surface or roughening a smoothsurface. Blasting may remove surface materials by forcibly propelling astream of abrasive material against a surface under high pressure.

The Al alloys described herein provide faster processing parameters thanconventional 7xxx series Al alloys, while maintaining properties such ascolor, hardness, and strength as described herein. As described above,the disclosed alloys differ from existing commercial 7xxx series alloysdue to the absence or reduced quantity of Zr, along with neutral color.Having a high extrusion productivity and low-quench sensitivity allowsfor reduction in Zr grain refinement, and a subsequent heat treatment isnot needed.

The 7xxx Al alloys disclosed herein have extrusion rates that are lessthan, but approaching, those of 6063 alloys. The extrusion times of theAl alloys are significantly higher than those of conventional 7xxx Alalloys. In some aspects, the extrusion rate alloys of the presentdisclosure are at least 70% of the processing time of a 6063 (T5) alloy.In some aspects, the extrusion rate of the disclosed alloys at least to75% of the processing time of a 6063 (T5) alloy. In still furtheraspects, the extrusion rate of the disclosed alloys are at least 80% ofthe processing time of a 6063 (T5) alloy.

The disclosed Al alloys are press-quenchable, and do not requirepost-extrusion heat treatment. Conventional 7xxx Al alloys that havehigher quantities of Zr ordinarily must be removed from the press andre-heated. By not undergoing the additional processing step ofre-heating, the presently disclosed alloys have a significant advantagein the time of manufacturing and cosmetic quality as compared toconventional Al alloys.

Further, the disclosed Al alloys are less quench sensitive than the 6063alloy. As a result, the disclosed Al alloys can be cooled more slowlythan conventional 7xxx series alloys before the properties of the alloys(such as strength and hardness) degrade. The disclosed Al alloys, andparts formed therefrom, can be cooled more slowly, while having betterextrusion and improved final part flatness.

In one example, parts produced from sample alloy 12 showed 30% improvedflatness and less quench distortion than those produced from samplealloy 1 (6063 alloy). As shown in FIG. 5, the hardness of sample alloy12 approached 140 HV when water quenched in a 25° water bath, and alsoremained above 130 HV when quenched in a 65 ° C. water bath, by forcedair cooling, or by air cooling. By comparison, the 6063 Al alloy neverexceeded 100 HV when cooled by similar methods. Sample alloy 12 showedreduced distortion by fan and air cooled alloys as compared to the 6063Al alloy (data not shown). Reduced distortion of the alloy providessignificant advantages in machining thinner and more intricate parts. Insum, the 7xxx Al alloys of the disclosure have a much larger processingwindow than the 6063 Al alloy and commercial 7xxx series Al alloys,while also allowing for improved strength, hardness, flatness, andcosmetic properties.

Various conventional 7xxx series Al alloys have a yellow color outsidethe range of colors described for alloys of the present disclosure,and/or a extrusion speed that is less than 20%, and alternatively lessthan 10%, of the processing time of certain 6063 (T5) alloys. Higherextrusion speeds translate practically to increased capacity ofmanufacturing. Other 7xxx series Al often result in additional heattreatment after extrusion. The increased extrusion time in which thealloy can be quenched out of the press without additional heat treatmentsteps, provide for faster manufacturing of the present alloys.

In further various aspects, the alloy has a tensile yield strength notless than 300 MPa, while also having extrusion speeds and/or neutralcolors as described herein.

Standard methods may be used for evaluation of cosmetics includingcolor, gloss, and haze.

Color

The color of objects may be determined by the wavelength of light thatis reflected or transmitted without being absorbed, assuming incidentlight is white light. The visual appearance of objects may vary withlight reflection or transmission. Additional appearance attributes maybe based on the directional brightness distribution of reflected lightor transmitted light, commonly referred to glossy, shiny, dull, clear,haze, among others. The quantitative evaluation may be performed basedon ASTM Standards on Color & Appearance Measurement or ASTM E-430Standard Test Methods for Measurement of Gloss of High-Gloss Surfaces,including ASTM D523 (Gloss), ASTM D2457 (Gloss on plastics), ASTM E430(Gloss on high-gloss surfaces, haze), and ASTM D5767 (DOI), amongothers. The measurements of gloss, haze, and DOI may be performed bytesting equipment, such as Rhopoint 10.

In some embodiments, color may be quantified by parameters L*, a*, andb*, where L* stands for light brightness, a* stands for color betweenred and green, and b* stands for color between blue and yellow. Forexample, high b* values suggest an unappealing yellowish color, not agold yellow color. Values near zero in a* and b* suggest a neutralcolor. Low L* values suggest dark brightness, while high L* valuesuggests great brightness. For color measurement, testing equipment,such as X-Rite Color i7 XTH, X-Rite Coloreye 7000 may be used. Thesemeasurements are according to CIE/ISO standards for illuminants,observers, and the L* a* b* color scale. For example, the standardsinclude: (a) ISO 11664-1:2007(E)/CIE S 014-1/E:2006: Joint ISO/CIEStandard: Colorimetry—Part 1: CIE Standard Colorimetric Observers; (b)ISO 11664-2:2007(E)/CIE S 014-2/E:2006: Joint ISO/CIE Standard:Colorimetry—Part 2: CIE Standard Illuminants for Colorimetry, (c) ISO11664-3:2012(E)/CIE S 014-3/E:2011: Joint ISO/CIE Standard:Colorimetry—Part 3: CIE Tristimulus Values; and (d) ISO11664-4:2008(E)/CIE S 014-4/E:2007: Joint ISO/CIE Standard:Colorimetry—Part 4: CIE 1976 L* a* b* Colour Space.

As described herein, reducing or eliminating Cu from the alloys providesthe alloy with neutral color. The alloys described herein include Mg₂Znto provide additional yield strength to the alloy. Alloys having theneutral color and low aspect ratios in the range 0.8-1.2 as describedherein. The L*a*b* corresponding neutral color resulting at least inpart from the alloy composition described herein is described herein.

In various aspects, the L* of the alloy disclosed herein is at least 85.In some instances, the L* of the alloy is at least 90.

The alloys disclosed herein have neutral color. Neutral color refers toa* and b* that does not deviate beyond certain values close to 0. Invarious aspects, a* is not less than −0.5. In various aspects, a* is notless than −0.25. In various aspects, a* is not greater than 0.25. Invarious aspects, a* is not greater than 0.5. In further aspects, a* isnot less than −0.5 and not greater than 0.5. In further aspects, a* isnot less than −0.25 and not greater than 0.25.

In various aspects, b* is not less than −2.0. In various aspects, b* isnot less than −1.75. In various aspects, b* is not less than −1.50. Invarious aspects, b* is not less than −1.25.

In various aspects, b* is not less than −1.0. In various aspects, b* isnot less than −0.5. In various aspects, b* is not less than −0.25. Invarious aspects, b* is not greater than 1.0. In various aspects, b* isnot greater than 1.25. In various aspects, b* is not greater than 1.50.In various aspects, b* is not greater than 1.75. In various aspects, b*is not greater than 2.0. In various aspects, b* is not greater than 0.5.In various aspects, b* is not greater than 0.25. In further aspects, b*is not less than −1.0 and not greater than 1.0. In further aspects, b*is not less than −0.5 and not greater than 0.5.

Yield strengths of the alloys may be determined via ASTM E8, whichcovers the testing apparatus, test specimens, and testing procedure fortensile testing.

Stress corrosion tests may be performed on the alloys via ASTM G47,which covers the test method of sampling, type of specimen, specimenpreparation, test environment, and method of exposure for determiningthe susceptibility to SCC of aluminum alloys.

In some embodiments, the present alloys can form enclosures for theelectronic devices. The enclosures may be designed to have a blastedsurface finish, or absence of streaky lines. Blasting is a surfacefinishing process, for example, smoothing a rough surface or rougheninga smooth surface. Blasting may remove surface materials by forciblypropelling a stream of abrasive material against a surface under highpressure.

In various embodiments, the alloys may be used as housings or otherparts of an electronic device, such as, for example, a part of thehousing or casing of the device. Devices can include any consumerelectronic device, such as cell phones, desktop computers, laptopcomputers, and/or portable music players. The device can be a part of adisplay, such as a digital display, a monitor, an electronic-bookreader, a portable web-browser, and a computer monitor. The device canalso be an entertainment device, including a portable DVD player, DVDplayer, Blue-Ray disk player, video game console, or music player, suchas a portable music player. The device can also be a part of a devicethat provides control, such as controlling the streaming of images,videos, sounds, or it can be a remote control for an electronic device.The alloys can be part of a computer or its accessories, such as thehard driver tower housing or casing, laptop housing, laptop keyboard,laptop track pad, desktop keyboard, mouse, and speaker. The alloys canalso be applied to a device such as a watch or a clock.

Having described several embodiments, it will be recognized by thoseskilled in the art that various modifications, alternativeconstructions, and equivalents may be used without departing from thespirit of the disclosure. Additionally, a number of well-known processesand elements have not been described in order to avoid unnecessarilyobscuring the embodiments disclosed herein. Accordingly, the abovedescription should not be taken as limiting the scope of the document.

Those skilled in the art will appreciate that the presently disclosedembodiments teach by way of example and not by limitation. Therefore,the matter contained in the above description or shown in theaccompanying drawings should be interpreted as illustrative and not in alimiting sense. The following claims are intended to cover all genericand specific features described herein, as well as all statements of thescope of the method and system, which, as a matter of language, might besaid to fall there between.

What is claimed is:
 1. An aluminum alloy comprising: 4.5 to 8.0 wt % Zn;0.9 to 2.0 wt % Mg; 0.01 to 0.3 wt % Cu; 0.04 to 0.25 wt % Fe; 0 to 0.05wt % Zr; and the balance being aluminum and incidental impurities. 2.The aluminum alloy according to claim 1, wherein the alloy has a wt %ratio of Zn to Mg from 4:1 to 7:1.
 3. The aluminum alloy according toclaim 1, comprising 0 to 0.04 wt % Zr.
 4. The aluminum alloy accordingto claim 1, comprising 0 to 0.10 wt % Si.
 5. The aluminum alloyaccording to claim 1, wherein the alloy has 3-6 vol % MgZn₂.
 6. Thealuminum alloy according to claim 1, wherein the alloy has an averagegrain aspect ratio of 1.0 to 1.3.
 7. The aluminum alloy according toclaim 1, wherein the alloy has a thermal conductivity greater than 130W/mk.
 8. The aluminum alloy according to claim 1, wherein the alloy hasa yield strength of at least 280 MPa.
 9. An aluminum alloy comprising:6.0 to 7.0 wt % Zn; 1.0 to 1.75 wt % Mg; 0.1 to 0.3 wt % Cu; 0.10 to0.20 wt % Fe; 0 to 0.05 wt % Zr; and the balance being aluminum andincidental impurities.
 10. The aluminum alloy according to claim 1,wherein the alloy has a wt % ratio of Zn to Mg from 4:1 to 7:1.
 11. Thealuminum alloy according to claim 1, wherein the alloy has 3-6 vol %MgZn₂.
 12. The aluminum alloy according to claim 1, wherein the alloyhas an average grain aspect ratio of 1.0 to 1.3.
 13. The aluminum alloyaccording to claim 1, wherein the alloy has a thermal conductivitygreater than 130 W/mk.
 14. The aluminum alloy according to claim 1,wherein the alloy has a yield strength of at least 280 MPa.
 15. Ahousing for an electronic device comprising the alloy comprising: 4.5 to8.0 wt % Zn; 0.9 to 2.0 wt % Mg; 0.01 to 0.30 wt % Cu; 0.04 to 0.25 wt %Fe; 0 to 0.05 wt % Zr; and the balance being aluminum and incidentalimpurities.
 16. The housing according to claim 15, wherein the alloyhaving a wt % ratio of Zn to Mg from 4:1 to 7:1.
 17. The housingaccording to claim 15, wherein the alloy has 3-6 vol % MgZn₂.
 18. Thehousing according to claim 15, wherein the alloy has an average grainaspect ratio of 1.0 to 1.3.
 19. The housing according to claim 15,wherein the alloy has a thermal conductivity greater than 130 W/mk. 20.The housing according to claim 15, wherein the alloy has a yieldstrength of at least 280 MPa.